U.S. patent application number 11/425219 was filed with the patent office on 2007-05-17 for spread spectrum radar apparatus.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Takeshi FUKUDA.
Application Number | 20070109175 11/425219 |
Document ID | / |
Family ID | 37689091 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070109175 |
Kind Code |
A1 |
FUKUDA; Takeshi |
May 17, 2007 |
SPREAD SPECTRUM RADAR APPARATUS
Abstract
A spread spectrum radar apparatus includes: a pseudo-noise code
generation unit that generates two or more transmitter pseudo-noise
codes which are respectively different and two or more receiver
pseudo-noise codes which are respectively different, based on a
timing signal; a spreading modulation unit that generates a spread
signal by modulating a signal having a predetermined frequency in
plural stages, using the two or more transmitter pseudo-noise codes
individually in the respective stages; a transmission unit that
emits the spread signal as the detection radio wave; a reception
unit that receives, as a received signal, the detection radio wave
reflected back from the object; a despreading modulation unit that
generates a despread signal by modulating the received signal,
using the two or more receiver pseudo-noise codes individually in
the respective stages; and a signal processing unit that detects
presence of the object in accordance with a signal intensity of at
least a specific frequency component, based on the despread
signal.
Inventors: |
FUKUDA; Takeshi; (Osaka,,
JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
1006, Oaza Kadoma, Kadoma-shi,
Osaka
JP
|
Family ID: |
37689091 |
Appl. No.: |
11/425219 |
Filed: |
June 20, 2006 |
Current U.S.
Class: |
342/70 ; 342/131;
342/132; 342/134; 342/137; 342/159; 342/71; 342/82; 342/85 |
Current CPC
Class: |
G01S 2013/93271
20200101; G01S 7/36 20130101; G01S 2013/93272 20200101; G01S 13/931
20130101; G01S 13/325 20130101 |
Class at
Publication: |
342/070 ;
342/071; 342/131; 342/132; 342/134; 342/137; 342/159; 342/082;
342/085 |
International
Class: |
G01S 13/08 20060101
G01S013/08; G01S 13/93 20060101 G01S013/93 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2005 |
JP |
2005/182616 |
Claims
1. A spread spectrum radar apparatus that detects an object by use
of a detection radio wave which is a spectrum-spread radio wave
used for object detection, said apparatus comprising: a
pseudo-noise code generation unit operable to generate two or more
pseudo-noise codes which are respectively different, based on a
timing signal; a spreading modulation unit operable to generate a
spread signal by modulating a signal having a predetermined
frequency in plural stages, using the two or more pseudo-noise
codes individually in the respective stages; and a transmission
unit operable to emit the spread signal as the detection radio
wave.
2. The spread spectrum radar apparatus according to claim 1,
wherein said pseudo-noise code generation unit is operable to
generate, as the two or more pseudo-noise codes, M sequence
codes.
3. The spread spectrum radar apparatus according to claim 1,
wherein said pseudo-noise code generation unit is operable to
generate, as the two or more pseudo-noise codes, M sequence codes
of a single type, the M sequence codes having respectively
different delay amounts and being generated based on the same
generating polynomial.
4. The spread spectrum radar apparatus according to claim 1,
wherein said pseudo-noise code generation unit is operable to
generate, as the two or more pseudo-noise codes, M sequence codes
of plural types, the M sequence codes being generated based on
respectively different generating polynomials.
5. A spread spectrum radar apparatus that detects an object by use
of a detection radio wave which is a spectrum-spread radio wave
used for object detection, said apparatus comprising: a
pseudo-noise code generation unit operable to generate two or more
pseudo-noise codes which are respectively different, based on a
timing signal; a reception unit operable to receive, as a received
signal, the detection radio wave reflected back from the object; a
despreading modulation unit operable to generate a despread signal
by modulating the received signal, using the two or more
pseudo-noise codes individually in the respective stages; and a
signal processing unit operable to detect presence of the object in
accordance with a signal intensity of at least a specific frequency
component, based on the despread signal.
6. The spread spectrum radar apparatus according to claim 5,
wherein said pseudo-noise code generation unit is operable to
generate, as the two or more pseudo-noise codes, M sequence
codes.
7. The spread spectrum radar apparatus according to claim 5,
wherein said pseudo-noise code generation unit is operable to
generate, as the two or more pseudo-noise codes, M sequence codes
of a single type, the M sequence codes having respectively
different delay amounts and being generated based on the same
generating polynomial.
8. The spread spectrum radar apparatus according to claim 5,
wherein said pseudo-noise code generation unit is operable to
generate, as the two or more pseudo-noise codes, M sequence codes
of plural types, the M sequence codes being generated based on
respectively different generating polynomials.
9. A spread spectrum radar apparatus that detects an object by use
of a detection radio wave which is a spectrum-spread radio wave
used for object detection, said apparatus comprising: a
pseudo-noise code generation unit operable to generate two or more
transmitter pseudo-noise codes which are respectively different and
two or more receiver pseudo-noise codes which are respectively
different, based on a timing signal; a spreading modulation unit
operable to generate a spread signal by modulating a signal having
a predetermined frequency in plural stages, using the two or more
transmitter pseudo-noise codes individually in the respective
stages; a transmission unit operable to emit the spread signal as
the detection radio wave; a reception unit operable to receive, as
a received signal, the detection radio wave reflected back from the
object; a despreading modulation unit operable to generate a
despread signal by modulating the received signal, using the two or
more receiver pseudo-noise codes individually in the respective
stages; and a signal processing unit operable to detect presence of
the object in accordance with a signal intensity of at least a
specific frequency component, based on the despread signal.
Description
BACKGROUND OF THE INVENTION
[0001] (1) Field of the Invention
[0002] The present invention relates to a radar apparatus utilizing
a spread spectrum scheme, and particularly relates to a
sophisticated spread spectrum radar apparatus with a high
capability of object detection.
[0003] (2) Description of the Related Art
[0004] In recent years, a considerable effort has been made on
technological development of radar apparatuses mounted on vehicles
(hereinafter referred to as "on-vehicle radar apparatuses"). For
example, there has been proposed a radar apparatus or the like
utilizing a spread spectrum scheme (hereinafter referred to as the
"spread spectrum radar apparatus") (for example, refer to Japanese
Laid-Open Patent Application No. 07-12930).
[0005] On-vehicle radar apparatuses are used for detection of a
preceding car, an obstacle located backward, and the like, for the
purpose of safety improvement such as collision avoidance and
enhancement of the driving convenience represented by reverse
driving support. When the on-vehicle radar apparatuses are used for
such purposes, it is necessary to suppress the influence of
undesired radio waves from another radar apparatus of the same
type. For example, interference by an electromagnetic wave emitted
from a radar apparatus of the same type mounted on another vehicle
should be suppressed.
[0006] In contrast, a spread spectrum radar apparatus is capable of
suppressing the influence of undesired radio waves since a radio
wave to be transmitted is modulated using a pseudo-noise code
(hereinafter referred to as the "PN code") for spectrum spreading
and thus a radio wave that has been modulated using a different
code is suppressed within the receiver. Similarly, undesired radio
waves emitted from a radar apparatus of another type in which no
code modulation is performed, are suppressed within the receiver.
Furthermore, since the radio wave to be transmitted is
frequency-spread using a PN code, it is possible to minimize the
electric power per unit frequency and thus to reduce the influence
on other wireless systems. It is also possible to freely set a
relationship between distance resolution and maximum detectable
range by adjusting the chip rate and code period of the PN code. It
is further possible to reduce the peak power since continuous
transmission of radio waves is possible. With the above features,
it is possible to use even a frequency band in which electric power
per unit frequency is set to low by laws and regulations.
[0007] FIG. 1 is a diagram showing a general structure of a spread
spectrum radar apparatus having superior features as described
above.
[0008] As shown in FIG. 1, the spread spectrum radar apparatus 300
includes a timing generation unit 301, a PN code generation unit
302, a signal source 303, a transmission spreading modulation unit
304, a transmission unit 305, a transmission antenna 306, a
reception antenna 307, a reception unit 308, a reception spreading
modulation unit 309, a signal processing unit 310, a distance
measurement code delay unit 311, and the like.
[0009] Next, an operation of the conventional spread spectrum radar
apparatus 300 is described. At the transmitter side, a narrow-band
signal generated by the signal source 303 is spectrum-spread over a
wide band by the transmission spreading modulation unit 304, using
a PN code generated by the PN code generation unit 302. Then, the
resulting radio wave goes into the transmission unit 305 having
functions such as frequency transform and amplification, and is
emitted from the transmission antenna 306 as an object detection
radio wave used for object detection. Here, the transmission
spreading modulation unit 304 is configured, in general, of a
biphase modulator (BPSK modulator) such as a balanced mixer. The
transmission spreading modulation unit 304 spreads the frequency
band of an input signal, by phase-modulating the input signal using
two phases of 0 degree and 180 degree. Through this spreading
modulation, it is possible to minimize the electric power per unit
frequency of the detection radio wave emitted from the transmission
antenna 306.
[0010] Next, at the receiver side, a detection radio wave reflected
from an object is received by the reception antenna 307. Then, the
received detection radio wave is goes through the reception unit
308 configured of a low-noise amplifier, a frequency transformer,
or the like, and is despread by the reception spreading modulation
unit 309, using a "PN code f"; which is obtained by the distance
measurement code delay unit 311 performing time delay on the "PN
code e" supplied to the transmission spreading modulation unit 304.
At this time, when there is a match between (i) a delay time that
corresponds to the round trip time delay of the detection radio
wave attributable to the distance to the object from which the
detection radio wave has been reflected (such an object is
hereinafter referred to as a "reflection object") and (ii) the
delay time produced by the distance measurement code delay unit
311, it indicates that the phase of the code included in the
"signal c" outputted from the reception unit 308 matches the phase
of the "PN code f" outputted from the distance measurement code
delay unit 311. Thus, the same signal as that of the "signal a"
outputted from the signal source 303 is reconstructed as the
"signal d" outputted from the reception spreading modulation unit
309, and the frequency components of the "signal d" becomes the
same as those of the "signal a" being a narrow-band signal.
Meanwhile, in the case where the delay time produced by the
distance measurement code delay unit 311 is different from the
round trip time delay of the detection radio wave, the signal
represented by the "signal d" remains in a state where its
frequency is spread over a wide band without being despread. It is
possible for the signal processing unit 310 to detect whether or
not there exists a reflection object at a location which is away by
a distance that corresponds to the delay time set in the distance
measurement code delay unit 311, by selectively detecting the
frequency components of the "input signal d" that are the same as
those of the "signal a" outputted from the signal source 303. Here,
even when there exist undesired radio waves emitted from another
radar apparatus and wireless apparatus using the same frequency
band, no signal is converted into a narrow-band signal by the
reception spreading modulation unit 309 other than the one
spread-modulated using the same code with the same phase as the "PN
code f" which is outputted from the distance measurement code delay
unit 311. This indicates that the above-described spread spectrum
radar apparatus has a favorable feature of not being seriously
affected by undesired radio waves when performing an object
detection operation.
[0011] However, such conventional technology has a problem that the
operation characteristics of the radar apparatus are deteriorated
due to the leakage of an input signal to an output at the
transmission spreading modulation unit 304 and the reception
spreading modulation unit 309. FIG. 2A to FIG. 2D are diagrams,
each showing the frequency components of a signal at each unit
shown in FIG. 1.
[0012] Here, the "signal b" outputted from the transmission
spreading modulation unit 304 includes, in actuality, components (a
narrow-band signal 353) leaked from a narrow-band signal 351
inputted to the transmission spreading modulation unit 304, in
addition to a spread signal 352. Since the peak power of the
narrow-band signal 353 is required to be within the limit of the
emission intensity of radio waves per unit frequency, stipulated by
laws and regulations, it is necessary to suppress the peak power of
the narrow-band signal 353 by, for example, providing an attenuator
in between the transmission antenna 306 and the transmission unit
305. As a result, the capability of object detection is
deteriorated since it is consequently necessary to control the
whole electric power to be transmitted, including signal components
which are necessary for object detection and which have been spread
over a wide band, in addition to suppressing the peak power of the
narrow-band signal 353. In other words, the leaked narrow-band
signal 353 seriously diminishes an intrinsic advantage of the
conventional spread spectrum radar apparatus of being able to
minimize a per-unit frequency electric power included in a
detection radio wave. Furthermore, the narrow-band signal, which
has been leaked from the transmitter side without undergoing
spreading modulation, is received also at the receiver side to be
despread. At this time, in the case where the input signal inputted
to the reception spreading modulation unit 309 synchronizes with
the pseudo-noise code, a narrow-band signal 354 is outputted from
the reception spreading modulation unit 309, whereas in the case
where those pseudo-noise codes do not synchronize with each other,
the narrow-band signal, which has been leaked from the transmitter
side without undergoing spreading modulation, leaks directly to an
output of the reception spreading modulation unit 309 (a
narrow-band signal 356), although such leakage is only a little
amount. Such leaked narrow-band signal 356 has not undergone the
spreading modulation that uses the PN codes, and is outputted
independently of the intrinsic operation of the conventional spread
spectrum radar apparatus of selectively receiving only a detection
radio wave which has undergone propagation delay by a specific
delay amount. As a result, the performance of object detection is
deteriorated.
[0013] FIG. 3 is a diagram showing the signal intensity of the
frequency components of the "signal d" outputted from the reception
spreading modulation unit 309 that are the same as those of the
"signal a" outputted from the signal source 303, the signal
intensity being illustrated in connection with the delay amount of
the distance measurement code delay unit 311. When the delay amount
equals to the propagation delay time of a detection radio wave, the
signal intensity increases (a signal 361) since the signal which
has been spread over a wide band as a detection radio wave is
despread so as to reconstruct the narrow-band signal. However, even
when the delay amount does not equal to the propagation delay time
of the detection radio wave, signals (signals 362 and 363) which
are generated due to the signal leakage at the transmission
spreading modulation 304 and the reception spreading modulation
309, are observed.
[0014] Here, when there are plural reflection objects, there occurs
a problem of becoming unable to perform object detection because a
signal from an object with a weaker reflective power is interfered
with by a leaked narrow-band signal included in a signal reflected
from an object with a stronger reflective power.
[0015] The above-described problems attributable the operation
characteristics can be fatal defects that impair safety since it
may become impossible to detect an object with a weaker reflective
power, such as a pedestrian at a close location, due to a stronger
signal reflected from an object with a stronger reflective power,
such as a heavy vehicle at a distant location.
SUMMARY OF THE INVENTION
[0016] In view of the above problems, it is an object of the
present invention to provide a sophisticated spread spectrum radar
apparatus with a high capability of object detection, the apparatus
being capable of suppressing leakage of a narrow-band signal.
[0017] In order to achieve the above object, a spread spectrum
radar apparatus of the present invention is a spread spectrum radar
apparatus that detects an object by use of a detection radio wave
which is a spectrum-spread radio wave used for object detection,
the apparatus including: a pseudo-noise code generation unit that
generates two or more pseudo-noise codes which are respectively
different, based on a timing signal; a spreading modulation unit
that generates a spread signal by modulating a signal having a
predetermined frequency in plural stages, using the two or more
pseudo-noise codes individually in the respective stages; and a
transmission unit that emits the spread signal as the detection
radio wave.
[0018] With this structure, since the leakage of a narrow-band
signal to a detection radio wave is suppressed, it is possible to
solve the following problems with the conventional spread spectrum
radar apparatus attributable to the leaked narrow-band signal: its
intrinsic advantage of being able to minimize a per-unit frequency
electric power included in a detection radio wave is seriously
diminished; and the object detection capability of the conventional
spread spectrum radar apparatus is deteriorated since the leaked
narrow-band signal requires it to control the whole electric power
to be transmitted, including signal components necessary for an
object detection operation, in order to satisfy the limit of the
emission intensity of radio waves per unit frequency stipulated by
laws and regulations.
[0019] Furthermore, in order to achieve the above object, the
spread spectrum radar apparatus of the present invention is a
spread spectrum radar apparatus that detects an object by use of a
detection radio wave which is a spectrum-spread radio wave used for
object detection, the apparatus including: a pseudo-noise code
generation unit that generates two or more pseudo-noise codes which
are respectively different, based on a timing signal; a reception
unit that receives, as a received signal, the detection radio wave
reflected back from the object; a despreading modulation unit that
generates a despread signal by modulating the received signal,
using the two or more pseudo-noise codes individually in the
respective stages; and a signal processing unit that detects
presence of the object in accordance with a signal intensity of at
least a specific frequency component, based on the despread
signal.
[0020] With this structure, even when a narrow-band signal is
leaked to a spectrum-spread detection radio wave, since components
of the narrow-band signal leaked to the detection radio wave are
suppressed through plural despreading processes performed at the
receiver side, it is possible to suppress a signal that is
outputted independently of an intrinsic radar operation of
selectively receiving, at the receiver side, only a radio wave
which has undergone propagation delay by a specific delay amount.
Therefore, it is possible to solve the problems with the
conventional spread spectrum radar apparatus of becoming unable to
perform object detection because a signal from an object with a
weaker reflective power is interfered with by a leaked narrow-band
signal included in a signal reflected from an object with a
stronger reflective power.
[0021] Note that the present invention may be embodied not only as
a spread spectrum radar apparatus, but also as a detection method
utilizing a spectrum-spread radio wave (such method is hereinafter
referred to as a spread spectrum detection method), and the
like.
[0022] As described above, according to the present invention, it
is possible to provide a spread spectrum radar apparatus with an
excellent capability of object detection, the apparatus being
capable of suppressing, at the transmitter side, the leakage of a
narrow-band signal that is irrelevant to a radar detection
operation to a detection radio wave as well as capable of
suppressing, at the receiver side, the leaked signal that is
outputted independently of an intrinsic radar operation of
selectively receiving only a radio wave which has undergone
propagation delay by a specific delay amount.
FURTHER INFORMATION ABOUT TECHNICAL BACKGROUND TO THIS
APPLICATION
[0023] The disclosure of Japanese Patent Application No.
2005-182616 filed on Jun. 22, 2005 including specification,
drawings and claims is incorporated herein by reference in its
entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] These and other objects, advantages and features of the
invention will become apparent from the following description
thereof taken in conjunction with the accompanying drawings that
illustrate a specific embodiment of the invention. In the
Drawings:
[0025] FIG. 1 is a diagram showing a structure of a spread spectrum
radar apparatus according to a conventional technology;
[0026] FIG. 2A is a diagram showing a frequency spectrum of a
signal from a signal source of the spread spectrum radar apparatus
according to the conventional technology;
[0027] FIG. 2B is a diagram showing a frequency spectrum of an
output signal from a transmission spreading modulation unit of the
spread spectrum radar apparatus according to the conventional
technology;
[0028] FIG. 2C is a diagram showing a frequency spectrum of an
output signal from a reception spreading modulation unit of the
spread spectrum radar apparatus according to the conventional
technology, in the case where an input signal inputted to the
reception spreading modulation unit synchronizes with a
pseudo-noise code;
[0029] FIG. 2D is a diagram showing a frequency spectrum of an
output signal from the reception spreading modulation unit of the
spread spectrum radar apparatus according to the conventional
technology, in the case where an input signal inputted to the
reception spreading modulation unit does not synchronize with a
pseudo-noise code;
[0030] FIG. 3 is a diagram showing the signal intensity of the
frequency components of the output signal from the reception
spreading modulation unit of the spread spectrum radar apparatus
according to the conventional technology that are the same as those
of a signal outputted from the signal source, the signal intensity
being illustrated in connection with the delay amount of a distance
measurement code delay unit;
[0031] FIG. 4 is a diagram showing the case where a spread spectrum
radar apparatus according to an embodiment of the present invention
is embodied as an on-vehicle radar apparatus;
[0032] FIG. 5 is a diagram showing a structure of the spread
spectrum radar apparatus according to an embodiment of the present
invention;
[0033] FIG. 6A is a diagram showing a frequency spectrum of a
signal from a signal source of the spread spectrum radar apparatus
according to the embodiment of the present invention;
[0034] FIG. 6B is a diagram showing a frequency spectrum of an
output signal from a first transmission spreading modulation unit
of the spread spectrum radar apparatus according to the embodiment
of the present invention;
[0035] FIG. 6C is a diagram showing a frequency spectrum of an
output signal from a second transmission spreading modulation unit
of the spread spectrum radar apparatus according to the embodiment
of the present invention;
[0036] FIG. 6D is a diagram showing a frequency spectrum of an
input signal of a despreading modulation unit of the spread
spectrum radar apparatus according to the embodiment of the present
invention;
[0037] FIG. 6E is a diagram showing a frequency spectrum of an
output signal of the despreading modulation unit of the spread
spectrum radar apparatus according to the embodiment of the present
invention, in the case where the phases of spreading codes
synchronize with each other;
[0038] FIG. 6F is a diagram showing a frequency spectrum of an
output signal of the despreading modulation unit of the spread
spectrum radar apparatus according to the embodiment of the present
invention, in the case where the phases of spreading codes do not
synchronize with each other;
[0039] FIG. 7 is a diagram showing the signal intensity of the
frequency components of the output signal from the despreading
modulation unit of the spread spectrum radar apparatus according to
the embodiment of the present invention that are the same as those
of a signal outputted from the signal source, the signal intensity
being illustrated in connection with the delay amount of a distance
measurement code delay unit;
[0040] FIG. 8 is a diagram showing a structure of a spread spectrum
radar apparatus according to another embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiment
[0041] The following describes a preferred embodiment of the
present invention with reference to the drawings.
[0042] The spread spectrum radar apparatus according to an
embodiment of the present invention is (a) a spread spectrum radar
apparatus that detects an object by use of a detection radio wave
which is a spectrum-spread radio wave used for object detection,
the apparatus (b) generating two or more transmitter pseudo-noise
codes which are respectively different and two or more receiver
pseudo-noise codes which are respectively different, based on a
timing signal, (c) generating a spread signal by modulating a
signal having a predetermined frequency in plural stages, using the
two or more transmitter pseudo-noise codes individually in the
respective stages, (d) emitting the spread signal as the detection
radio wave, (e) receiving, as a received signal, the detection
radio wave reflected back from the object, (f) generating a
despread signal by modulating the received signal, using the two or
more receiver pseudo-noise codes individually in the respective
stages, and (g) detecting the presence of the object in accordance
with a signal intensity of at least a specific frequency component,
based on the despread signal.
[0043] For example, as shown in FIG. 4, the spread spectrum radar
apparatus according to the present embodiment is equipped at the
front and tail of a vehicle 11. The spread spectrum radar apparatus
emits a detection radio wave for object detection to an object such
as a preceding vehicle 12 and an obstruction 13, receives a
detection radio wave reflected from the object, and determines the
presence/absence of an obstruction, a distance from the
obstruction, and a relative speed, based on the received detection
radio wave.
[0044] Based on the above points, the spread spectrum radar
apparatus of the present embodiment is described hereafter.
[0045] First, the structure of the spread spectrum radar apparatus
of the present embodiment is described.
[0046] As shown in FIG. 5, a spread spectrum radar apparatus 100
includes a timing generation unit 101, a pseudo-noise code
generation unit 102, a signal source 103, a spreading modulation
unit 104, a transmission unit 105, a transmission antenna 106, a
reception antenna 107, a reception unit 108, a despreading
modulation unit 109, a signal processing unit 110, and the
like.
[0047] Furthermore, the pseudo-noise code generation unit 102
includes a PN code generation unit 121, a transmission code delay
unit 122, a distance measurement code delay unit 123, a reception
code delay unit 124, and the like.
[0048] The PN code generation unit 121 generates a "pseudo-noise
code (hereinafter also referred to as a "PN code") e" based on a
timing signal generated by the timing generation unit 101.
[0049] The transmission code delay unit 122 outputs a "PN code e'",
which is different from the "PN code e", by delaying the "PN code
e" generated by the PN generation unit 121.
[0050] The distance measurement code delay unit 123 outputs a "PN
code f", which is different from the "PN code e", by delaying the
"PN code e" generated by the PN generation unit 121.
[0051] The reception code delay unit 124 outputs a "PN code f'",
which is different from the "PN code f", by delaying the "PN code
f" outputted from the distance measurement code delay unit 123.
[0052] At the transmitter side, the spreading modulation unit 104
performs spread spectrum modulation on a narrow-band signal
generated by the signal source 103, using the PN code generated by
the pseudo-noise code generation unit 102, so as to convert it into
a wide-band signal. After this, the transmission unit 105 performs
signal processing, such as frequency transform and amplification,
on the wide-band signal where necessary. The resulting signal is
outputted from the transmission antenna 106 as an object detection
radio wave. At the receiver side, the reception antenna 107
receives a detection radio wave reflected from the object. Then,
the reception unit 108 performs processing, such as low-noise
amplification and frequency transform, on the received detection
radio wave where necessary. The despreading modulation unit 109
performs despreading modulation on the resulting radio wave, using
the code obtained by the distance measurement code delay unit 123
by delaying the pseudo-noise code generated by the pseudo-noise
code generation unit 102. The signal processing unit 110 selects
the same frequency components as those included in the signal
generated by the signal source 103 at the transmitter side, from
among the frequency components included in the "signal d'"
outputted from the despreading modulation unit 109, and detects the
presence/absence of the object by measuring the intensity of such
selected components.
[0053] Here, the spreading modulation unit 104 includes a first
transmission spreading modulation unit 141, a second transmission
spreading modulation unit 142, and the like. With this structure,
even when there is the same level of leakage of an input signal at
the first transmission spreading modulation unit 141 as the leakage
occurring in the transmission spreading modulation unit 304 of the
conventional spread spectrum radar apparatus 300, the second
transmission spreading modulation unit 142 at the second stage
makes it possible to achieve a dramatic reduction, on the whole
spreading modulation unit 104 level, in the amount of the leakage
of the "narrow-band input signal a" to the "output signal b'". For
example, consider the case where general doubly balanced mixers are
used as the first transmission spreading modulation unit 141 and
second transmission spreading modulation unit 142. In the case
where only one doubly balanced mixer is used, isolation between the
input side and the output side is some 20 dB, whereas in the case
where two serially-connected doubly balanced mixers are used, the
whole isolation is 40 dB, thereby reducing the leakage of electric
power to the output side to one-hundredth of the conventional
technology.
[0054] Moreover, the despreading modulation unit 109 includes a
first reception spreading modulation unit 191, a second reception
spreading modulation unit 192, and the like. According to the same
operating principle as that of the spreading modulation unit 104,
this structure makes it possible to achieve a dramatic suppression
of signal components leaking from the input side to the output side
on the whole despreading modulation unit 109 level. For example,
consider the case where general doubly balanced mixers are used as
the first reception spreading modulation unit 191 and second
reception spreading modulation unit 192. In the case where only one
doubly balanced mixer is used, isolation between the input side and
the output side is some 20 dB, whereas in the case where two
serially-connected doubly balanced mixers are used, the whole
isolation is 40 dB, thereby reducing the leakage of electric power
to the output side to one-hundredth of the conventional
technology.
[0055] Here, a description is given of the principle according to
which the spread spectrum radar apparatus of the present invention
measures a distance.
[0056] In the spread spectrum radar apparatus 100, plural spreading
modulation units are serially connected, as in the case of the
first transmission spreading modulation unit 141 and the second
transmission spreading modulation unit 142 of the spreading
modulation unit 104, and different pseudo-noise codes are provided
to the respective spreading modulation units so as to perform
multi-stage spreading modulation.
[0057] This structure makes it possible to achieve an ideal
processing result with reduced signal leakage that occurs between
the input side and the output side in each of the transmission
spreading modulation units. Moreover, the result to be obtained
through spreading modulation performed by the spreading modulation
unit 104 is substantially the same as the result obtained by
performing a single-stage spreading modulation on an input signal,
using a single code obtained by performing exclusive OR on
pseudo-noise codes (spreading codes) provided to the respective
transmission spreading modulation units.
[0058] In the transmitter side, as codes used for spreading
modulation, a "PN code e" generated by the single PN code
generation unit 121 is used by the first transmission spreading
modulation unit 141 to perform spreading modulation, after which a
"PN code e'" obtained by the transmission code delay unit 122
delaying the same "PN code e" is used by the second transmission
spreading modulation unit 142 to perform spreading modulation. As a
result, the "output signal b'" is substantially obtained by
performing spreading modulation on an "input signal a" using a code
that is obtained by performing exclusive OR on the "PN code e" and
the "PN code e'" obtained by delaying the "PN code e".
[0059] More specifically, as shown in FIG. 6A, when receiving an
input of the "signal a" from the signal source 103, i.e., a
narrow-band signal 151, the first transmission spreading modulation
unit 141 spreads the narrow-band signal 151, using the "PN code e"
provided from the PN code generation unit 121, and outputs the
"signal b".
[0060] When this is done, as shown in FIG. 6B, the "signal b"
outputted from the first transmission spreading modulation unit 141
includes a narrow-band signal 153, which is the leakage of the
narrow-band signal 151 provided from the signal source 103, in
addition to a spread signal 152 actually obtained through spreading
modulation.
[0061] Also, when receiving an input of the "signal b" outputted
from the first transmission spreading modulation unit 141, i.e.,
the spread signal 152 and narrow-band signal 153, the second
transmission spreading modulation unit 142 spreads the spread
signal 152 and the narrow-band signal 153, using the "PN code e'"
outputted from the transmission code delay unit 122, and outputs
the "signal b'".
[0062] When this is done, as shown in FIG. 6C, the "signal b'"
outputted from the second transmission spreading modulation unit
142 includes a narrow-band signal 155, which is a small leakage of
the narrow-band signal 153 provided from the first transmission
spreading modulation unit 141, in addition to a spread signal 154
actually obtained through spreading modulation.
[0063] Here, in the case where an M-sequence code is used as the
"PN code e", an "output signal b'" is substantially obtained as the
result of performing a single-stage spreading modulation on the
"input signal a", using a code that is obtained by delaying the
original "PN code e". Thus, the use of an M-sequence code makes it
possible to directly inherit a feature of M-sequence code that is
desirable from the standpoint of operations of the radar apparatus,
such as excellent autocorrelation.
[0064] Such a feature is based on the following property: an
exclusive OR between an M-sequence code generated from a certain
generating polynomial and another M-sequence code that has a
different phase and that is generated from the same generating
polynomial results in a code obtained by delaying the original
M-sequence code. In other words, the above feature is based on the
property that an exclusive OR between the original M-sequence code
and a code obtained by delaying the original M-sequence code
results in a code obtained by delaying the original M-sequence
code. Through the use of such mathematical characteristics of
M-sequence code, even when multi-stage spreading modulation is
performed, the same result is obtained as that of performing a
single-stage spreading modulation using an M-sequence code that is
different from the original M-sequence code only in phase. Thus, it
is possible to inherit excellent features of M-sequence code.
[0065] Furthermore, supposing that the isolation between the input
and output sides in each of the first transmission spreading
modulation unit 141 and the second transmission spreading
modulation unit 142 is some 20 dB, it is possible to reduce the
electric power of the narrow-band signal 155 to one hundredth
compared to the narrow-band signal 151, and thus to minimize the
influence caused by components that leak without being spread.
[0066] At the receiver side too, on the similar principle, while
suppressing signal leakage between the input and output sides on
the whole despreading modulation 109 level by performing two-stage
despreading modulation through the first reception spreading
modulation unit 191 and the second reception spreading modulation
unit 192, the same result is substantially obtained as that
obtained by performing a single-stage despreading modulation using
a code that is obtained by delaying the "PN code f".
[0067] More specifically, as shown in FIG. 6D, when receiving an
input of the "signal d" outputted from the first reception
spreading modulation unit 191, i.e., the spread signal 156 and
narrow-band signal 157, the second reception spreading modulation
unit 192 despreads the spread signal 156 and the narrow-band signal
157, using the "PN code f'" outputted from the reception code delay
unit 124, and outputs the "signal d'".
[0068] When this is done, when autocorrelation is obtained while
changing the delay amount by the distance measurement code delay
unit 123, a narrow-band signal 158 is reconstructed as shown in
FIG. 6E. On the other hand, when autocorrelation is not obtained, a
signal including a spread signal 159 and a narrow-band signal 160
is obtained as shown in FIG. 6F.
[0069] Through the above principle, signal processing to be
performed is substantially the same as that of the conventional
spread spectrum radar apparatus, although multi-stage spreading
modulation is performed at the transmitter side or multi-stage
despreading modulation is performed at the receiver side.
Therefore, in the case where the delay amount of a substantial
receiver spreading code corresponding to a substantial transmitter
spreading code equals to the propagation delay amount of an object
detection radio wave, the object detection radio wave spread over a
wide band is to be despread, and the narrow-band signal generated
by the signal source 103 at the transmitter side is reproduced as
the "signal d'" outputted from the despreading modulation unit 109.
The signal processing unit 110 can detect the presence of an object
by selectively detecting the frequency components that are included
in the frequency components generated by the signal source 103, out
of the frequency components included in the "signal d'" outputted
from the despreading modulation unit 109.
[0070] For example, as shown in FIG. 7, when the delay amount
equals to the propagation delay time of a detection radio wave, the
signal intensity increases (a signal 161) since the signal which
has been spread over a wide band as a detection radio wave is
despread so as to reconstruct the narrow-band signal. Furthermore,
thanks to the suppression of signal leakage, it is possible to
observe a signal which is hidden behind a leaked signal in the
conventional technology (a signal 162), and thus the capability of
object detection improves.
[0071] Here, time delay between the PN code e provided to the
transmitter side and the transmitter spreading code corresponding
to a substantially single-stage spreading modulation performed by
the spreading modulation unit 104, is uniquely determined by the
delay amount applied by the transmission code delay unit 122, and
time delay between the "PN code f" provided to the receiver side
via the distance measurement code delay unit 123 and a substantial
receiver spreading code corresponding to a substantially
single-stage despreading modulation performed by the despreading
modulation unit 109, is uniquely determined by the delay amount
applied by the reception code delay unit 124. Thus, by taking into
consideration these delay amounts in advance, it is possible to
determine the propagation delay time of an object detection radio
wave corresponding to the delay time set to the distance
measurement code delay unit 123.
[0072] In particular, by using the same delay amount for the delay
amount applied by the transmission code delay unit 122 and for the
delay amount applied by the reception code delay unit 124, it is
possible to set the same time difference for the time difference
between the "PN code e" and the substantial transmitter spreading
code in the spreading modulation unit 104 and for the time
difference between the "PN code f" and the substantial receiver
spreading code in the despreading modulation unit 109. Thus, it is
possible to make a direct association between the round trip time
delay of the object detection radio wave and delay time set to the
distance measurement code delay unit 123.
[0073] As described above, the spread spectrum radar apparatus of
the present embodiment has an excellent capability of object
detection since it is capable of suppressing, at the transmitter
side, the leakage of a narrow-band signal that is irrelevant to a
radar detection operation to a detection radio wave as well as
capable of suppressing, at the receiver side, the leaked signal
that is outputted independently of an intrinsic radar operation of
selectively receiving only a radio wave which has undergone
propagation delay by a specific delay amount.
[0074] (Others)
[0075] Note that M sequence codes generated from respectively
different generating polynomials may be provided to the respective
spreading modulation units in the multi-stage spreading modulation.
In this case, the result to be substantially achieved is the one
obtained by performing a single-stage spreading modulation using a
code that is generated through linear combination of these M
sequence codes. Such a code generated through linear combination of
plural M sequence codes generated from different generating
polynomials is referred to as a gold code. The use of gold code
makes it possible to generate many mutually independent sequences,
and thus to provide a favorable feature of being able to realize
many radar apparatuses which do not interfere with each other.
[0076] Furthermore, other codes than the codes described above may
be used in the multi-stage spreading modulation. In this case, any
codes may be used to allow enjoy the advantage, serving as an
essential feature of the present invention, of being able to
suppress signal leakage between the input and output sides, as long
as the autocorrelation characteristics of a substantial spreading
code that is generated through exclusive OR between codes provided
to the respective spreading modulation units in the multi-stage
spreading modulation, are suited to radar operations.
[0077] Moreover, although the above-described embodiment of the
present invention presents an example case where two-stage
spreading modulation is carried out both at the transmitter side
and the receiver side, it is possible to improve the performance of
the radar apparatus on the whole, as long as multi-stage spreading
modulation units are structured in at least one of the transmitter
side and the receiver side. For example, it is possible that
two-stage spreading modulation units are structured only at the
transmitter side and a single-stage spreading modulation unit is
structure at the receiver side.
[0078] Furthermore, the respective spreading modulation units may
be integrated with frequency transform. For example, as shown in
FIG. 8, the following structure may be employed: a local oscillator
244 is provided at the transmitter side; a transmission spreading
modulation unit 243 generates a "signal E''" by spreading a "local
oscillation signal G" from the local oscillator 244 using a
"spreading code E'"; and a second spreading modulation unit 242
performs spreading modulation on an "input signal B" using the
"signal E''"; so as to generate an "output signal B'". In this
case, although spreading to be performed using the "spreading code
E'" and frequency transform to be performed using the "local
oscillation signal G" are carried out in an integrated manner, this
integration can be used as an operation of one of the spreading
modulation units of the present invention, since spreading
modulation is substantially performed on the "input signal B",
using the "spreading code E'".
[0079] Similarly, as shown in FIG. 8, the following structure may
be employed: a local oscillator 294 is provided also at the
receiver side; a reception spreading modulation unit 293 generates
a "signal F''" by spreading a "local oscillation signal H" from the
local oscillator 294 using a "spreading code F"; and a first
reception spreading modulation unit 291 performs spreading
modulation on an "input signal C", using the "spreading code F''",
so as to generate an "output signal D". In this case, although
spreading to be performed using the "spreading code F" and
frequency transform to be performed using the "local oscillation
signal H" are carried out in an integrated manner, this integration
can be used as an operation of one of the spreading modulation
units of the present invention since spreading modulation is
substantially performed on the "input signal C", using the
"spreading code F".
[0080] Note that the present invention may be embodied not only as
a spread spectrum radar apparatus, but also as a detection method
utilizing a spectrum-spread radio wave, and the like.
[0081] Also note that the present invention may not only be
embodied as a single unit spread spectrum radar apparatus but also
separately as the transmitter function and as the receiver function
of the spread spectrum radar apparatus.
[0082] Moreover, the despreading modulation unit 109 may only
include at least one spreading modulation unit as long as the
spreading modulation unit 104 includes two or more spreading
modulation units which are serially connected. In other words, as
long as the "output signal b'" is generated at the transmitter side
through plural spreading processes, the "output signal d'" may be
generated through a single despreading process at the receiver side
without having to undergo plural despreading processes. This
structure makes it possible to perform plural spreading processes
on a leaked narrow-band signal at the transmitter side and to
suppress such narrow-band signal before it is emitted as a
detection radio wave.
[0083] Similarly, the spreading modulation unit 104 may only
include at least one spreading modulation unit as long as the
despreading modulation unit 109 includes two or more spreading
modulation units which are serially connected. In other words, as
long as the "output signal d'" is generated at the receiver side
thorough plural despreading processes, the "output signal b'" may
be generated at the transmitter side through a single spreading
process without having to undergo plural spreading processes. This
structure makes it possible to perform plural despreading processes
on a leaked narrow-band signal that has not been spread at the
receiver side and to suppress such narrow-band signal before it is
inputted into the signal processing unit 110.
[0084] Although only an exemplary embodiment of this invention has
been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiment without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention.
INDUSTRIAL APPLICABILITY
[0085] The present invention is applicable for use as a
sophisticated spread spectrum radar apparatus with a high
capability of object detection.
* * * * *